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Functions of spleen and lymph nodes

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Reticuloendothelial system• phagocytosis – ingestion of microbes or foreign cells or solid materials by a phagocyte• phagocytes are neutrophils, monocytes & macrophages• monocytes transform themselves into macrophages in tissue• these macrophages are mononuclear cells, & this system of phagocytes is called as mononuclear phagocyte system (MPS)• this system of cells was known as reticuloendothelial system – neither they are reticular in appearance – nor they have endothelial origin• Therefore, the term reticuloendothelial system is obsolete.

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Macrophages (Kupffer cells) in the liver sinusoids bacteria from ingested food pass through GIT into the portal blood ↓ it passes through the sinusoids of the liver ↓ these sinusoids are lined with Kupffer cells ↓ these cells form an effective particulate filtration system

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Alveolar macrophages in the lungs• organisms enter the body through the lungs• macrophages can phagocytize particles 1. if the particles are digestible, the macrophages can digest them & release the digestive products into the lymph 2. if the particle is not digestible, the macrophages often form a “giant cell” capsule around the particle→ slowly dissolve

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Microglia of brain• microglia cells in brain & spinal cord appear to be inactive• in inflammatory disease of the CNS, they become the immune effector cells• they proliferate & become antigen presenting cells

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Tissue macrophages in the lymph nodes• if the particles are not destroyed locally in the tissues, they enter the lymph & flow to the lymph nodes• foreign particles are then trapped in these nodes in a meshwork of sinuses lined by tissue macrophages

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Tissue macrophages in the spleen & bone• if an invading organism succeeds in entering the general circulation, there are other lines of defense

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Mesangial cells in kidney• are an unusual example of phagocytic cells derived from smooth muscle & not monocytes• aid neutrophils in removing other mesangial cells undergoing apoptosis & also other debris in glomerulus

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Tissue macrophages in the skin & subcutaneous tissues (Histiocytes)• when infection begins in a subcutaneous tissue & local inflammation ensues, local tissue macrophages can divide in situ & form still more macrophages• then they perform the usual functions of attacking & destroying the infectious agents

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Functions of spleen• Formation of blood cells – play in important role in the hemopoietic function in embryo – during the hepatic stage, spleen produces the blood cells along with liver• Destruction of blood cells – the older RBCs, lymphocytes & thrombocytes are destroyed in the spleen

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• Reservoir function – a large number of RBCs are stored in spleen – RBCs are released form spleen into circulation during the emergency conditions like hypoxia & hemorrhage• Role in defense of body – spleen filters the blood by removing the microorganism – macrophages in splenic pulp phagocytose the microorganism & other foreign bodies – spleen contains about 25% of T lymphocytes & 15% of B lymphocytes & form the site of antibody production

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Functions of lymph nodesLymph nodes serve as filters which filter bacteria & toxicsubstances form the lymph.• when lymph passes through the lymph nodes, it is filtered i.e. the water & electrolytes are removed – but the proteins & lipids are retained in the lymph• bacteria & other toxic substances are destroyed by macrophages of lymph nodes